You might want to look into the "German-American Bund", very likely the Nazi group that was doing it. There were some chapters around here (NJ) and they managed to make a nuisance of themselves and not much else.
I've done some research in the midwest and discovered that the Bund was active throughout that part of our country. This fact serves as the background for my second novel: The Twins, and will continue to be background for my third, now in process. I'm very interested in discussing this topic with anyone.